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ARLINGTON, Va. - Some came in dress uniforms crowded with rows of military decorations, and some wore T-shirts and tennis shoes. Some wore black, as if attending a funeral. All wore red, white, and blue ribbons pinned to their lapels, and all but the youngest among them sat in quiet silence at 9:37 a.m.

Yesterday’s ceremony at the Pentagon marked the moment 10 years ago when a hijacked jetliner carved a swath of destruction through the headquarters of the nation’s military. It was in many ways a dual observance, mourning not only the deaths inflicted by Al Qaeda in 2001 but also the sacrifice of those killed in the two wars spawned by the attack.

There was no mistaking Osama bin Laden’s intent when he targeted the seat of US military power, said Vice President Joe Biden, who called the Pentagon “this great citadel of our national defense.’’

“Those in this building that day knew what they were witnessing: It was a declaration of war, by stateless actors bent on changing our way of life, who believed that these horrible acts - these horrible acts of terror - directed against innocents, could buckle our knees, could bend our will, could begin to break us, break our resolve,’’ Biden said. “They did not know us.’’

About 1,600 people, most of them family of those killed and injured in the attack, marked the occasion. Before the ceremony, some strolled through the nearby memorial plaza, where a bench marks each of the 59 passengers and crew and 125 inside the Pentagon who died when American Airlines flight 77 smashed into the building.

Many used programs as fans or as a shield from the punishing sun, and after the moment of silence, a US Navy chorus quietly sang “Amazing Grace.’’ Behind the dais, a three-story-tall flag hung from the Pentagon’s roof in the same place where a similar flag was unfurled 10 years ago.

Biden, along with Defense Secretary Leon E. Panetta and the chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, traced the arc of the US military since that day, linking the attacks to those who have since died in Iraq and Afghanistan.

The ceremony was as much an opportunity to mourn as to demonstrate resolve. Panetta said that after a decade, “the wounds are still present, the emotions still raw,’’ but the attacks showed the strength and courage of those left behind and those who donned uniforms in its aftermath.

“We will never forget the human cost paid by this generation, the more than 6,200 soldiers, sailors, airmen, Marines lost in the line of duty. Like those taken from us on 9/11, we will always remember that they paid the ultimate sacrifice for America,’’ he said.

After the speeches, service members laid individual wreaths for each of the people who died that day. The ceremony closed with the mournful strains of taps from an Army Band bugler. Later in the day, President Obama laid a wreath at the site and greeted well-wishers.

In another grim reminder, jets from nearby Ronald Reagan Washington National Airport streamed overhead, occasionally drowning out the speakers as the planes climbed into the sky.

Donn Marshall, whose wife Shelley was killed Sept. 11, grimaced at the sound. He was at work in nearby Crystal City when the plane struck; their two young children were in the Pentagon’s day care center and were unharmed. They moved back to Marshall’s native West Virginia in 2003.

“I don’t have to hear that sound,’’ he said, gesturing at the plane passing overhead. “That sound reminds me of 9/11 every time I hear it.’’

Marshall, who has since remarried, said he wished the nation could regain the unity it showed after the attacks. “You look at where we are now, and there’s discord. We were a unified nation, and now it’s like we’re warring tribes. That bothers me.’’

In nearby Arlington National Cemetery, some marked the anniversary with visits to gravesites. Alison Malachowski, 55, of Westminster, Md., visited the grave of her son James, a 25-year-old Marine staff sergeant killed in Afghanistan in March.

“It’s a living hell,’’ Malachowski said between tears. “Every parent always wonders how horrifying it would be if their child was killed. I can tell you, it’s a million times worse than you could ever imagine. I never wake up from the nightmare of losing my son.’’

Phillip Boos, 49, of Saxonburg, Pa., wore his Navy whites as he visited the grave of his friend Robert Schlegel, who was a 38-year-old Navy commander when he was killed at the Pentagon on Sept. 11.

Boos stared for a while at the grave, which was adorned with a bouquet of red, white, and blue flowers. He took a gold key chain from his pocket and placed it atop the headstone, and saluted the grave of his fallen comrade.

“He was a great guy,’’ Boos said. “One of those guys you just wanted to be around. Good humor and a quick wit. He was one of the best of us. It’s just a damn shame.’’

Globe correspondent Alex Katz contributed to this report. Theo Emery can be reached at TEmery@globe.com